Abstract
In-situ stress measurement using the Kaiser effect of AE (Acoustic Emission) was adapted to investigate the underground stress conditions. Most rocks are porous to some degree. If the pores of in-situ rock contain pore water, rocks (in-situ rock mass) are subjected to in-situ stress and furthermore pore water pressure. However the influence of pore water pressure on the Kaiser effect has not been studied. In this study, we performed experiments to clarify the influence of pore water pressure on the Kaiser effect using sandstone. Firstly, uniaxial compressive stress was re-loaded after triaxial compressive pre-loading with several pore water pressures. Secondly, triaxial compressive re-loading was performed under different several pore water pressures after triaxial compressive pre-loading with pore water pressure. Two points having rapidly increasing cumulative AE event count were observed. The two stresses of 1st and 2nd Kaiser effect points were then compared with pre-effective axial stress and pre-differential stress. The estimated stresses were very close to those pre-stresses, and not influenced by pore water pressure in pre-loading and re-loading.
